The present invention pertains to an arrangement with a control circuit for controlling a numerical value for patient respiration as well as to the control of the numerical value.
The control of the flow of a flowing medium, especially a gas, by means of valves via a cascade control circuit is described in EP 483 401 B1. It can be used for the respiration of humans and animals for the valve-controlled supply and removal of a gaseous anesthetic. The control parameter of the first control circuit is the flow, and the position of the valves or the current and the voltage for actuating the valves may be the control parameters of the second control circuit.
A device and a process for the automation of peripheral anesthesia, which are based on measured values determined on the patient, have been known from EP 236 513 A1. The metering of anesthetics is preferably controlled there on the basis of an electromyelogram by means of electrodes distributed locally on the patient. However, the anesthetic is administered by local infusion rather than via a respiration circuit. The additional recording of an electroencephalogram of the patient is used for monitoring in order to prevent unconsciousness of the patient, which is undesirable in the case of peripheral anesthesia.
An anesthesia apparatus of this type with breathing circuit and control circuits for components of the gaseous anesthetic is described in DE 40 04 034 C2. System parameters of the breathing circuit are determined there from the changes in the concentrations of the gaseous anesthetic over time and setting parameters for the anesthetic controller are calculated from these. The changes in the concentration of a gaseous anesthetic over time in the breathing circuit depend, e.g., on the amount of the gaseous anesthetic component flowing in, the volume of the breathing circuit and the gas circulation within the breathing circuit. Due to a need-adapted adjustment of the settling parameters, which are calculated from the changes in the concentration over time, the controller furnishes time-optimized setting values. The drawback of this and other prior-art anesthesia respirators is that the control of the gaseous anesthetic components is performed only on the basis of the system parameters of the breathing circuit. As a result, the control is complicated and slow, it requires frequent calibration and is not adapted to the individual patient.
The object of the present invention is to make an arrangement for controlling a numerical value for patient respiration and a process for controlling the numerical value simpler and more rapid and at the same time to make possible a need-adapted adjustment for the respiration of the individual patient.
According to the invention an arrangement with a control circuit for controlling a numerical value for patient respiration is provided. The arrangement has a respiration circuit for delivering a gaseous anesthetic mixture to the lungs of a patient connected thereto via a Y-piece. A unit for EEG control is provided with an EEG sensor connected to the brain of the patient via head electrodes for measuring an EEG actual value, a EEG set point transducer for sending an EEG set point, an EEG comparison point, which forms the difference between the EEG actual value and the EEG set point, and an EEG controller. The controller forms a manipulated variable from the difference for a metering device for at least one anesthetic in the gaseous anesthetic mixture, so that when the EEG set point is exceeded by the EEG actual value, the percentage of at least one anesthetic in the gaseous anesthetic mixture is increased by the metering device. When the EEG actual value drops below the EEG set point, the percentage of at least one anesthetic in the gaseous anesthetic mixture is reduced by the metering device until the EEG actual value and the EEG set point agree.
The control circuit for controlling the inspiratory gaseous anesthetic concentrations may be cascaded to the control circuit for controlling the numerical value. The EEG controller forms a set point for a gaseous anesthetic comparison point, to which the inspiratory gaseous anesthetic concentrations determined by a gaseous anesthetic sensor are sent as the actual value and which forms the difference between the actual value and the set point, from the difference between the EEG actual value and the EEG set point instead of forming the manipulated variable for the metering device and for a gaseous anesthetic controller, which generates a manipulated variable for the metering device from the difference.
The arrangement may have a changeover switch that either switches on the unit for the EEG control with the cascaded control circuit for controlling the inspiratory gaseous anesthetic concentrations and switches off a unit for controlling the expiratory gaseous anesthetic concentrations or switches off the unit for the EEG control with the cascaded control circuit for controlling the inspiratory gaseous anesthetic concentrations and switches on the unit for controlling the expiratory gaseous anesthetic concentrations when no EEG actual value of the EEG sensor is available over a predetermined time period. The unit for controlling the expiratory gaseous anesthetic concentrations comprises the gaseous anesthetic sensor for measuring an actual value of the expiratory gaseous anesthetic concentrations, a gaseous anesthetic set point transducer for sending a set point for the expiratory gaseous anesthetic concentrations, a gaseous anesthetic comparison point, which forms the difference between the actual value and the set point, and a gaseous anesthetic controller, which forms a manipulated variable from the difference for the metering device, so that when the actual value drops below the set point, the percentage of at least one anesthetic in the gaseous anesthetic mixture is increased by the metering device and when the set point is exceeded by the actual value, the percentage of at least one anesthetic in the gaseous anesthetic mixture is reduced by the metering device until the actual value and the set point agree.
The control circuit for controlling a numerical value may be switched off and a corresponding gaseous anesthetic mixture may be metered into the respiration circuit, presetting inspiratory gaseous anesthetic concentrations via the metering device, when the values of the EEG or of the expiratory gaseous anesthetic concentrations are outside predetermined tolerance ranges.
The gaseous anesthetic sensors may be infrared optical gas sensors.
According to another aspect of the invention, a process is provided in which an EEG actual value is measured by a EEG sensor. An EEG set point is sent by a EEG set point transducer. The difference is formed at a EEG comparison point from the EEG actual value and the EEG set point. A manipulated variable is generated from the difference by a EEG controller for a metering device for at least one anesthetic in the gaseous anesthetic mixture so that when the EEG set point is exceeded by the EEG actual value, the percentage of at least one anesthetic in the gaseous anesthetic mixture is increased by the metering device and when the EEG actual value drops below the EEG set point, the percentage of at least one anesthetic in the gaseous anesthetic mixture is reduced by the metering device until the EEG actual value and the EEG set point agree.
According to another aspect of the invention, an arrangement is provided with a control circuit for controlling a numerical value for patient respiration. The arrangement includes a respiration circuit for delivering a gaseous anesthetic mixture to the lungs of a patient connected thereto via a Y-piece. A unit for controlling a physiological parameter of the patient includes a sensor for measuring an actual value of the physiological parameter of the patient, a set point transducer for the physiological parameter of the patient for sending a set point for the physiological parameter of the patient, a comparison point for the physiological parameter of the patient, which forms the difference between the actual value of the physiological parameter of the patient and the set point of the physiological parameter of the patient, and a controller for the physiological parameter of the patient. The controller forms from the difference a manipulated variable for the metering means for at least one anesthetic in the gaseous anesthetic mixture. When the set point of the physiological parameter of the patient is exceeded by the actual value of the physiological parameter of the patient, the percentage of at least one anesthetic in the gaseous anesthetic mixture is increased by the metering means, and when the actual value of the physiological parameter of the patient drops below the set point of the physiological parameter of the patient, the percentage of at least one anesthetic in the gaseous anesthetic mixture is reduced by the metering means until the actual value of the physiological parameter of the patient and the set point of the physiological parameter of the patient agree.
The advantage of the present invention is that a gaseous anesthetic mixture can be metered for the patient directly according to the patient""s needs with a control circuit for controlling a numerical value on the basis of the evaluation of the EEG (electroencephalogram).
In a preferred embodiment, a control circuit for controlling the inspiratory gaseous anesthetic concentration in the manner of a cascade circuit is cascaded to the control circuit for controlling the numerical value. An especially rapid control of the numerical value is thus made possible.
If the EEG needed for controlling the numerical value, preferably the BIS (bispectral index), is not available over a certain time period, switching over to a control circuit for controlling the numerical value on the basis of the expiratory gaseous anesthetic concentration is possible in another advantageous embodiment of the present invention.
If the control of the numerical value cannot be performed reliably either on the basis of the EEG or on the basis of the expiratory gaseous anesthetic concentration, a safety precaution is taken according to the present invention in such a way that the gaseous anesthetic mixture is metered at an inspiratory gaseous anesthetic concentration preset automatically or by the user while all control circuits are switched off.
Besides the control of a numerical value on the basis of an evaluation of the EEG at the patient, the evaluation of other physiological parameters of the patient is also conceivable. A control circuit for controlling the inspiratory gaseous anesthetic concentration in the manner of a cascade circuit may also be cascaded to a control circuit for controlling a numerical value on the basis of the evaluation of another physiological parameter of the patient.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.